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OPA735: the power consumption of the REF5025 and OPA735

kevin.wang
Prodigy 165 points
Part Number: OPA735
Other Parts Discussed in Thread: ADS1282, , REF6250, REF5050

hello sir

 I want to used ref5025 and OPA735 for my ADS1282 circuit to get +2.5V and -2.5V for the voltage reference. But I found the current of the circuit is too big. the total current of power supply is 15mA, and the power consumption is 51mw in no load，how can i reduce the current of the circuit，can you give me some suggestion to design the circuit？

best regards！

kevin

 

 

  • 0
    Guru 140200 points
    Hi Kevin,

    you must not connect a cap directly from the output of OPA735 to GND. This will erode the phase margin and can make the OPA735 oscillate. This would explain the increased current consumption.

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 44620 points

    @ Kai, That is a great observation, thank you!

    Hi Kevin,

    I think Kai may be onto something... Looking at the typical quiescent currents of these devices and the loading, I would expect the total current consumption to be between 7-9 mA, so an oscillation on the output of the op-amp could be increasing the overall power consumption.

     

    An additional suggestion to reduce the power consumption, would be to modify your circuit such that you could remove the op-amp altogether (this probably saves maybe ~0.5 mA)... Typically, you would generate a -2.5V supply from a switching converter + LDO (it seems you already have a -3.3V supply so an additional LDO would be required). This supply would then become the "ground reference" for a 5V reference (such as the REF5050 or REF6250), then the output of this voltage reference would be at 2.5V. NOTE: This solution also requires that you have a supply voltage in your system that is just slightly greater than 5V (5.5V, 6V) in order to power the 5V reference source. If this is not already available, then perhaps this implementation would not be much of a current savings; however, I still think it is a good option to consider.

     

  • 0 in reply to Christopher Hall
    TI__Guru 63770 points
    Other potential solutions of generating dual polarity voltage references by level shifting voltage reference are discussed in the blog below:

    e2e.ti.com/.../understanding-voltage-references-level-shift-of-precision-voltage-references